In the C++ programming language, the namespace that contains the standard library. It is not clear how to pronounce it, but in many conferences you will hear it either spelled, “ess-tee-dee”, for instance like the chair of the ISO C++ Committee Herb Sutter, or pronounced like “stud” or “stood”. Or you can just say “standard”, if you are not in a hurry.
A poll made by engineer J. F. Bastien suggests that spelling is the most popular option.